Despite his ‘man of the people’ persona, he has promised more tax cuts for the rich in UKIP’s 2015 manifesto.

Tax cuts: Nigel Farage (Photo: FameFlynet.uk.com)

Labour said his comments on a hung Parliament come as no surprise.

“UKIP is a party joined at the hip to the Conservatives by Tory policy, Tory politicians and Tory money,” blasted Shadow Cabinet Minister Michael Dugher.

“They are more Tory than the Tories.”

No surprise: Michael Dugher (Photo: PA)

The UKIP U-turn comes after a weekend poll found one in four voters now say they back the anti-Europe party.

Experts said UKIP could win anything between 12 and 128 seats in Westminster if the Survation poll for the Mail on Sunday, putting them on 25% of the vote, is borne out next May.

The poll heaps massive pressure on Mr Cameron, who has already lost two MPs to UKIP and is now braced for further defections.

Four Conservative MPs have been told they have more chance of keeping their seat if they quit the Tories and join UKIP.

And in a direct attack on the PM’s authority, London Mayor Boris Johnson - favourite to be the next Tory leader – has blamed Mr Cameron for a “big deception” over immigration.

The Tory Mayor said Mr Cameron should never have promised to cut annual immigration to below 100,000-a-year.

It has since soared to more than double that rate.

“We said we could control the numbers, and we couldn’t,” Mr Johnson said.

Attack: Boris Johnson (Photo: BBC)

It is the latest brickbat for Mr Cameron since the Tories were trounced by UKIP in last week’s Clacton by-election.

An unnamed Cabinet Minister said a second defeat to UKIP, this time in Rochester and Strood, would see rattled Tory backbenchers trigger a leadership contest.

The senior Minister said a victory for turncoat MP Mark Reckless in next month’s by-election would be enough to convince the required number of Tory MPs - 46 - to sign a letter triggering a leadership vote.

“If Reckless wins Rochester, there will be 46 names,” the Cabinet Minister warned.

“Cameron would win. But it would be very damaging.”

Defeat in another by-election would also heighten the prospect of further Tory defections to UKIP.

Reckless warning: Nigel Farage (Photo: REUTERS)

A new study by politics expert Professor Matthew Goodwin concluded four Tory MPs would be more likely to keep their seat if they abandon their party.

Amber Valley MP Nigel Mills, Cleethorpes MP Martin Vickers, Bury North MP David Nuttall and Dudley South MP Chris Kelly were all told they could increase their vote share by defecting to UKIP.

Ironically his stance was effectively backed by London Mayor Mr Johnson, who admitted there is little to choose between the Tories and UKIP.

The top Tory described the two parties as “doppelgangers” who want the same things.

Quit: Mark Reckless with Nigel Farage (Photo: PA)

In a message to “beloved Kippers” Mr Johnson said: “It doesn’t seem to me there is a lot between us.”

In a bid to win back support, the London Mayor even said he would be happy to campaign for Britain to leave the EU if major reform is rejected by other foreign leaders.

“You’ve got to be willing to walk away,” he said.

But he insisted the rise of UKIP was as much to do with Mr Cameron’s false promises on cutting immigration as the large numbers of eastern European migrants who moved to Britain during the last decade.

“There were two big deceptions,” Mr Johnson said. “The first was when (Tony) Blair took the brakes off in 2004.

“Other countries kept their borders sealed and we didn’t.

“That was a mistake - and the other thing was saying we could control the numbers and we couldn’t.”